SEWPCC Upgrading/Expansion Preliminary Design Report SECTION 4 - POPULATION AND FLOW PROJECTIVES. Table of Contents

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1 SEWPCC Upgrading/Expansion Preliminary Design Report SECTION 4 - POPULATION AND FLOW PROJECTIVES Table of Contents 4.0 POPULATION AND FLOW PROJECTIONS POPULATION FORECAST Source Data Method of Projection Population Factors Affecting Population Projection Population Projection Envelopes Population Forecast for SEWPCC Service Area Overview of SEWPCC Service Area Population Distribution SEWPCC Population Projection FLOW FORECASTS Dry-Weather Flow (DWF) Projection Overall Winnipeg Water Use Trends SEWPCC Historic DWF Residential Water Use Projections Projecting Per Capita SEWPCC Wastewater Generation SEWPCC DWF Projection DWF Diversions Hourly DWF Peaking Wet-Weather Flow (WWF) Projections Introduction Policy Decision Frequency Analysis Flow Frequency Distribution in 2031 Based on Historic Data Analysis Accounting for Potential Sanitary Sewer Overflows (SSO) Estimated Hourly Wet-Weather Peak Sensitivity Analysis of Limiting I/I in New Areas WWF Diversions Maximum and Minimum Flows i

2 POPULATION FORECAST Wastewater flow projections are the basic parameters for determining SEWPCC expansion requirements. Sizing of system components, such as treatment facilities, requires realistic wastewater-flow projections. Dry- and wet-weather flow projections are required for this purpose. Population forecasting is the first step in developing flow projections. The population data referenced in this report is based on the population data available at the time the report was prepared. The details of steps used in developing population forecasts are described in Section 2. Section 3 and Section 4 describe dry- and wet-weather flow projections, respectively. Based on the current design considerations, the year 2031 is the design year for the proposed SEWPCC treatment plant expansions. The longer period up to 2050 is also considered for the purpose of overall system evaluations beyond the year Source Data Table 4.1 indicates the sources of existing data used for the overall City of Winnipeg population projection. Table 4.1 Existing Database of Winnipeg Population Between 1921 and 2026 Data Date Source and Method Historic COW Environmental Planning Department Historic COW Projection Conference Board of Canada (derived by taking 92.3% of Census Metropolitan Area), September 2004 Extrapolated from the Conference Board of Canada Note: Census Metropolitan Area (CMA) includes COW and municipalities of Richot, Tache, Springfield, East St. Paul, West St. Paul, Rosser, St. Francois Xavier, Headingley, St. Clements and Brokenhead First Nation Method of Projection Population The overall City of Winnipeg base population projection for the years was developed by the City of Winnipeg based on estimates of age distribution and net migrations during this 4.1

3 period. The present study considered the same demographics and net migration factors to extrapolate Winnipeg s population to 2031 and beyond to 2050 as demonstrated in Figure ,000, , ,000 Population 700, , , ,000 Historic Data ( ) Extrapolated by COW ( ) Extrapolated by TCI ( ) 300, , Year Figure TetrES Extrapolation of City of Winnipeg Population Forecast ( ) Factors Affecting Population Projection Net migration is a significant factor affecting Winnipeg s population growth as shown in Figure 4.2. Net migration is the difference between the number of people moving to Winnipeg each year and the number of people leaving. If net migration is positive, then the number of people migrating to Winnipeg is greater than the number migrating from Winnipeg. 4.2

4 8,000 6,000 4,000 Net Migration 2, ,000-4,000-6, Historic Data ( ) Extrapolated by COW from Conference Board of Canada ( ) -8,000 Year Figure Existing Data for Net Migration (Statistics Canada: The Conference Board of Canada; derived by taking 92.3% of CMA) The Conference Board projection shows overall net migration increasing from approximately 2,200 per year (in 2006) to 4,400 per year by This is much higher than the historic average and therefore assumes stronger economic growth into the future. The study team estimated the net migration trend to increase from 4,420 per year in 2027 to 7,700 per year in This projection was estimated by extrapolating the Conference Board of Canada net migration data between 2006 and 2026 (Figure 4.2). Another population projection scenario considers a stable net migration in which the growth rate remains constant at 4,420 per year from 2027 to 2050 as illustrated in Figure

5 8,000 6,000 Proposed Design Period (2031) ,000 Net Migration 2, ,000-4,000-6, Historic Data ( ) Extrapolated by COW from Conference Board of Canada ( ) Stable Net Migration Extrapolated by TCI ( ) -8,000 Year Figure Net Migration Projections Population Projection Envelopes Population projection envelopes are used to identify the reasonable range for overall population projection. In this study, the population projection envelopes are developed based on the following scenarios (Figure 4.4): 1. Low net migration rate (50% of mid-net migration) 2. Mid-net migration rate (Conference Board projections extended to 2050) 3. High net migration rate (150% of mid-net migration) 4.4

6 Net Migration 12,000 Proposed Design Period (2031) 10,000 Mid Net Migration Rate 8,000 High Net Migration Rate 6,000 Low Net Migration Rate 4,000 2, ,000-4,000-6,000-8, Year Figure Net Migration Range Figure 4.5 shows the results of overall population forecasts for the City of Winnipeg when different net migration rates are applied. Based on the assumptions made regarding net migration rates, Winnipeg s population is expected to increase consistently over time. The average annual rate of growth is about 0.7% per year. The population estimate for 2031 ranges between 754,000 and 807,300 (see Table 4.2), while corresponding percent increase ranges between 16% and 24%, respectively. The stable migration scenario shows that if net migration was to remain constant, the population growth rate would slow. In 2050, the stable migration scenario is just below the lower limit of the projection envelope. 4.5

7 1,000, , ,000 Mid Net Migration Low Net Migration Rate High Net Migration Rate Stable Net Migration Proposed Design Period (2031) Population 700, , ,000 Historic Data ( ) ,000 Extrapolated by Extrapolated by COW ( ) TCI ( ) 300, , Year Figure Population Forecast for the City of Winnipeg This study utilizes the mid-range projection that estimates Winnipeg s population at 780,700 in Table 4.2 Overall Population Forecast (Entire City) Category 2005* (estimate) Stable Net Migration Rate 2031 Population % Growth ( ) , ,500 18% 825,600 27% % Growth ( ) Low Net Migration Rate 652, ,000 16% 832,900 28% TCI Mid-Range Net Migration Rate 652, ,700 20% 876,300 34% High Net Migration 652, ,300 24% 919,700 41% Rate Note: *projected from 2001 to

8 4.1.5 Population Forecast for SEWPCC Service Area Overview of SEWPCC Service Area The SEWPCC service area is the second largest service area in Winnipeg; however, it has the greatest potential for growth. There are large areas within the SEWPCC service area for population growth within Winnipeg (Figure 4.6). A coarse estimate of the current developed area in the SEWPCC is about 6,500 ha (excluding parks). The ultimate developed area is about 15,000 ha. Assuming about 5% of the area will remain undeveloped and the population density remains the same, the ultimate population in the service area would be about 400,000. Figure Map of Overall WPCC Service Areas 4.7

9 Population Distribution To determine the SEWPCC population growth, an understanding of historic and projected distribution of population growth between the three WPCC service areas is required. A number of sources were reviewed to determine the historic distribution of population growth within the City. Figure 4.7 illustrates the historic population from 1971 to 2001, based on service area (Memorandum from Chris Tait, July 20, 1999; and 2001 census data). The SEWPCC service area has received 63% of the City s new population growth during this period. 500, , ,000 NEWPCC (21% of Growth) 350,000 Population 300, , , , ,000 SEWPCC (63% of Growth) WEWPCC (16% of Growth) 50, Year Figure Historic Population Estimate Based on Service Area (City of Winnipeg 1999) The single-family dwelling permits by neighbourhood from 2003 and 2004 were reviewed to determine recent trends in population distribution (see Figure 4.8). 4.8

10 Figure Single-Family Dwelling Permits by Neighbourhood (Jan/03 to Jun/04) (City of Winnipeg Residential Land Supply Study Oct/04) Between 2003 and 2004, the SEWPCC service area had the largest portion of single-family permits (69%), while the NEWPCC and WEWPCC service areas had 27% and 4% permits, respectively. Table 4.3 summarizes the percent distribution based on each service area. 4.9

11 SEWPCC UPGRADING/EXPANSION Table 4.3 Summary of Single-Family Permits Based on Service Area Location SEWPCC NEWPCC WEWPCC Number of Dwelling Permits 3,320 1, % Distribution 69% 27% 4% The City of Winnipeg Planning Department has projected the most likely areas of development across the City for the years 2005 to Figure 4.9 illustrates the long-term City of Winnipeg planning distribution for residential development. Figure Forecasted Residential Development ( ) (City of Winnipeg, December 2005) 4.10

12 In long-term residential development ( ) plan, the distribution of population towards the SEWPCC area will increase over time from 2005 to Beyond 2021, the study team has projected that about 70% of new population growth will be in the SEWPCC service area. After 2021, the SEWPCC service area will still have considerable land available for development (see Table 4.6). Methods used to allocate the population distribution to the SEWPCC service area are summarized in Table 4.4. Table 4.5 summarizes the population distributions among service areas for the historic and future planning periods. Table 4.4 Allocation of Population Distribution to the SEWPCC Service Area Distribution Period Method of Allocation 1971 to 1996 Historic trend from COW data 1996 to 2001 Census 2001 data 2001 to to 2004 housing permits 2005 to to 2011 estimated projection from COW planning 2012 to to 2021 estimated projection from COW planning 2022 to to 2050 estimated projection from TCI Table 4.5 Summary of Population Distribution by Service Area Location Historic 1 ( ) Estimated Projection from Planning Dwelling Permits ( ) (TCI this study) 4 SEWPCC 63% 69% 42% 57% 70% NEWPCC 21% 27% 44% 19% 10% WEWPCC 16% 4% 14% 24% 20% 4.11

13 1. Revised estimated based on current Information, based on the COW Water and Wastewater Dept., memo from Chris Tait, July 20, Planning, Property, and Development Planning and Land Use Division, COW Residential Land Supply Study, October COW Forecasted Residential Land Development Study (Draft), December TetrES Consultants Inc. (this study). High and low estimates of new population growth distributed to the SEWPCC service area were identified in order to provide an indication of the range of population that the SEWPCC may need to serve. A variance of +/-5% was assigned for the development period from 2005 to 2011, while a wider variance of +/-10% was assigned for the period from 2012 to Table 4.6 summarizes the low, mid and high population distribution percentages used in this study. Table 4.6 Potential Population Distribution Range for the SEWPCC Service Area Development Period Low Population Distribution to SEWPCC Mid Population Distribution to SEWPCC High Population Distribution to SEWPCC % 42% 47% % 57% 67% % 70% 80% The five combinations of migration rates and distribution percentages used in this study to develop SEWPCC population projections are as follows: 1) Low net migration rate and low population distribution. 2) Mid net migration rate and low population distribution. 3) Mid net migration rate and mid population distribution. 4) Mid net migration rate and high population distribution. 5) High net migration rate and high population distribution. 4.12

14 Note that Scenarios 2, 3 and 4 use the mid net migration rate which was chosen for future design purposes. Scenarios 1 and 5 are considered in order to identify potential upper and lower bounds on the estimated population in the SEWPCC service area SEWPCC Population Projection Figure 4.10 illustrates a comparison of current population projections for the SEWPCC service area and previous COW projections from The current City population projection is slightly higher, while the SEWPCC population projection is similar. 950, ,000 New COW Total Population Projection (2004) 750,000 Population 650, , , ,000 High population distribution to SEWPCC TCI Old Total COW Population Projection (2003) Mid population distribution to SEWPCC 250,000 Historic Data Low population 150,000 distribution to SEWPCC Old COW Projection (2003) 50, Year Figure 4.10 Comparison of Population Forecasts for SEWPCC Service Area with Previous Projection Figure 4.11 shows the population forecasts for the SEWPCC service area based on the five combinations of net migration and population distribution listed above. 4.13

15 Population 500, , , , , ,000 Proposed Design Period (2031) Mid net migration rate and low population distribution High net migration rate and high population distribution 200,000 Historic Data Mid net migration rate and mid population distribution 150,000 Mid net migration rate and low population distribution 100,000 Low net migration rate and 50,000 low population distribution Year Figure Population Forecasts for SEWPCC Service Area In 2031, the population growth for SEWPCC service area ranges between 28% and 56% (see Table 4.7). The scenario with low migration rate and low population growth results in the lowest population increase of 229,800 by 2031, while the high migration rate and high population growth scenario produces the highest population increases at 281,000. The scenarios using a mid migration rate combined with low and high population growth result in the SEWPCC service area population projects of approximately 241,900 and 264,600 respectively by

16 Table 4.7 Summary of Population Forecast for SEWPCC Service Area Option Low migration rate with low population distribution to SEWPCC 2005* 2031 Population Distribution for SEWPCC % Growth ( ) 2050 % Growth ( ) 179, ,800 28% 278,100 55% Low population growth 179, ,900 35% 301,900 68% Mid-net migration and population distribution to SEWPCC High population growth High migration rate with high population distribution to SEWPCC *projected from 2001 to , ,300 41% 323,300 80% 179, ,600 47% 344,700 92% 179, ,000 56% 376, % In the July 6, 2006 Workshop, the City expressed concerns that if the population growth was not as high as projected by the middle projection, the SEWPCC would be overbuilt. Selecting a lower projection provides more flexibility and allow for further expansion at a later date. In response to the City of Winnipeg direction provided at the July 6, 2006 workshop, the lowest migration rate with low population distribution option has been selected for developing dry- and wet-weather flow projections. The design population is selected at 229,800 in the year FLOW FORECASTS Dry-Weather Flow (DWF) Projection Overall Winnipeg Water Use Trends The historic citywide pumping records were reviewed to estimate per capita water use. Figure 4.12 illustrates citywide average daily water use (million litres per day ML/d) in January from 1955 to

17 Water Use (MLD) Year Figure Winnipeg Average Daily Water Use in January ( ) The daily per capita water use (litres per capital per day lcd) was calculated for each year and is shown in Figure Dry-weather wastewater generation within the City of Winnipeg is driven by water use, therefore, wastewater generation in winter should show the same general trend as water use. 500 Per Capita Water USe (lcd) Year Figure Winnipeg Water Use per Capita in January ( ) 4.16

18 The historic Winnipeg water use (Figure 4.12) has significantly increased over the decades from a low of 129 ML/d in 1955 to a peak of 275 ML/d in 1990, and had gradually dropped to about 211 ML/d by the end of Per capita water demand (Figure 4.13) has also shown a significant downward trend in the past 15 years despite increasing population SEWPCC Historic DWF Figure 4.14 illustrates SEWPCC DWF from 1983 to This figure shows that there has been no growth in DWF over the past 15 years. However, the population within this service area has grown over the past 15 years, and therefore, the per capita wastewater generation has decreased substantially, as shown in Figure Pumping Volume (MLD) Year Figure Average Daily SEWPCC Pumping Records in December and January ( ) 4.17

19 360 Wastewater Generation (lcd) Year Figure SEWPCC Average Daily Wastewater Generation per Capita in January and December ( ) The citywide trend for per capita water use and the SEWPCC per capita wastewater generation rates are very similar, both showing significant decreases over the past 15 years. Wastewater generation by residential, commercial, and industrial sectors was estimated using the City of Winnipeg Water Conservation Database for the SEWPCC service area (see Table 4.8). To obtain the per capita demand for each water use sector requires verification and summation of individual customer account readings. The method requires obtaining actual utility-read or self-read meter readings and excluding estimates developed by the utility for billing purposes. Since many occupants are not read every quarter, it may take a couple of years before an accurate sector estimate can be obtained. Total wastewater flows are measured daily at each WPCC; therefore, this analysis performed (last column in Table 4.8) is more up to date. This analysis shown in the table was performed in 2006 based on the information provided by the City in early The water consumption sector estimates and the infiltration estimate (wastewater flow minus water consumption) can only be estimated to the year 2003 at this time. 4.18

20 Table 4.8 Water Use Record for SEWPCC Service Area (Winnipeg Water Account COW Water Conservation Database, ) Year Residential (lcd) Commercial (lcd) Industrial and other (lcd) Total Water Consumption (lcd) Infiltration (lcd) Total SEWPCC Wastewater Base Flow (lcd) *Mid-winter per capita wastewater generation for the SEWPCC used an estimate of the population that does not include Windsor Park The residential water consumption has decreased over time from a high of 218 lcd in 1993 to as low as 208 lcd in The commercial and industrial water consumptions vary from year to year with slight declining trend since The winter infiltration rate was estimated by subtracting per capita water use from SEWPCC per capita pumping rates. This infiltration rate is variable from year to year Residential Water Use Projections Residential water usage is a driving factor for SEWPCC wastewater generation. In order to project residential wastewater use in the future, this study used the residential water use model developed by TetrES and the City of Winnipeg Water and Waste Department in Technology change that impacts water-using appliances such as toilets, is expected to play a major role in reducing water consumption across the City and in the SEWPCC service area. For example, changing technology could reduce per capita toilet water use from 73 lcd in 1992 to 30 lcd in 2046 (see Figure 4.16). Figure 4.17 illustrates the projected transition of toilets used in residences across the SEWPCC area. The effect of new construction using more efficient toilets and a renovation rate of 6% per year has been assumed to develop this projection. 4.19

21 Residential Indoor Water Use Cleaning (2 ) Cooking/Drinking (2 ) Dishwasher (7 ) Washers (41 ) 1992 (228 LCD) Toilets (73 ) Faucets (20 ) Bath (23 ) Toilet Leaks (14 ) Showers (46 ) Cleaning (2 ) Cooking/Drinking (2 ) Dishwasher (7 ) Washers (41 ) 2004 (217 LCD) Toilets (59 ) 2019 (196 LCD) Faucets (20 ) Toilet Leaks (14 ) Cleaning (2 ) Bath (23 ) Cooking/Drinking (2 ) Dishwasher (7 ) Toilets (41 ) Showers (49 ) Washers (37 ) Faucets (20 ) Toilet Leaks (14 ) 2046 (174 LCD) Cleaning (2 ) Bath (23 ) Showers (48 ) Cooking/Drinking (2 ) Dishwasher (7 ) Toilets (30 ) Washers (33 ) Toilet Leaks (14 ) Faucets (20 ) Bath (23 ) Showers (42 ) Figure 4.16 Effects of Technology Change (TetrES 1998) 4.20

22 Percent of Type 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% Year 22 Litres/Flush 13 Litres/Flush 6 Litres/Flush Figure Transition in Toilets Used Toilets account for a large portion of indoor water consumption, therefore, replacing the existing toilets using 22 litres/flush or 13 litres/flush with those using 6 litres/flush is expected to reduce future per-capita wastewater generation in the SEWPCC area Projecting Per Capita SEWPCC Wastewater Generation Commercial water usage was estimated approximately at 45 lcd, which is lower than the citywide water usage of 75 lcd in The trend of 45 lcd is expected to remain constant in the future. The industrial water usage was estimated at only 15 lcd, which is much lower than the citywide average industrial water usage of 50 lcd in This trend is also expected to remain constant in the future. In this projection, it is assumed that mid-winter infiltration will remain at 48 lcd into the future. The effects of technology change are taken into consideration for the residential water projection. The key components of residential water usage are toilets, showers, bath, faucets, washers, dishwasher, cooking/drinking and cleaning. Figure 4.18 shows the projected per capita usage for various components of residential water use. 4.21

23 lcd Per Capita Demand (lcd) Data 0% renovation rate Year Figure Long-Term Residential per Capita Water Demand (0% renovation rate) Overall residential per capita water use trend (0% renovation rate) for the SEWPCC service area is expected to be relatively constant with a slightly decreasing trend by the end of 2050 (Figure 4.18) from 222 lcd in 1993 to 208 lcd in After 2050, it is assumed that there will be no growth in per capita demand. Figure 4.19 illustrates a comparison of different renovation rates for residential per capita water demand projection. 4.22

24 lcd 220 Per Capita Demand (lcd) Data 0% renovation rate 2% renovation rate 4% renovation rate 6% renovation rate 190 lcd 176 lcd 169 lcd Year Figure Effect of Renovation Activities on Residential per Capita Water Demand Projection It is evident that home renovation plays a key role in residential water usage in which higher rate of home renovation decreases residential per capita water demand. The estimate water demand for different renovation rates is illustrated in Table 4.9. Table 4.9 Effect of Home Renovation on Residential per Capita Demand Option Estimated SEWPCC Projections lcd in % renovation rate 213 2% renovation rate 190 4% renovation rate 176 6% renovation rate

25 In 2031, the estimate of residential per capital demand based on different renovation rates ranges between 169 lcd and 213 lcd, respectively. The scenario with 0% renovation rate results in the highest per capital water demand of 213 lcd, while the 6%/year renovation rate scenario produces the lowest per capital water demand of 169 lcd. While 6%/year renovation rate provides the best fit to the short term data presented (see Figure 4.20), the participants in the July 6, 2006 Workshop considered it prudent to use a lower renovation rate of 2%/year. In response to the City of Winnipeg direction provided at the July 6, 2006 workshop, the 2% renovation rate option (190 lcd) has been selected for estimating residential per capital demand projection. SEWPCC per capita wastewater generation, including residential, commercial, and industrial sources and base infiltration is shown in Figure This figure illustrates that wastewater generation is expected to decrease from 323 lcd in 2006 to 298 lcd in SEWPCC (lcd) January Pumpage (lcd) Model 298 lcd Year Figure Total SEWPCC per Capita Projection 4.24

26 SEWPCC DWF Projection Using the population projections and the per capita DWF projection, DWF estimates for the 2031 design year and up to 2050 were developed as shown in Figure Total SEWPCC Wastewater Projection 90 Wastewater (MLD) Model January Pumpage (MLD) 68.4 MLD Year Figure SEWPCC DWF Projection to 2050 (including Windsor Park) Figure Location and Size of Combined Sewer Districts DWF is projected to increase over time from the present value of 50.4 ML/d (including Windsor Park in 2005) to 68.4 ML/d in 2031 using a population of 229,800 and a per capita, wastewater usage of 298 lcd. This trend continues, producing a DWF or 79.3 ML/d in DWF Diversions As noted in Table 4.9, the SEWPCC service area DWF projection is based on the assumption that the Windsor Park District will be in the SEWPCC service area continuously in the future. This study also looked at scenarios in which Windsor Park is diverted to the NEWPCC either in the winter time, or continuously, and in addition, what the impact would be if the combined sewer districts (that is Cockburn, Baltimore, Mager and Metcalf) are also diverted. Figure 4.22 illustrates the location and relative size of these Districts in the SEWPCC service area. 4.25

27 56 42 N Combined Sewer Boundary b ha 2 20a ha ha ha ha 57 COMBINED SEWER DISTRICTS 1 ALEXANDER 2 ARMSTRONG 3 ASH 4 ASSINIBOINE 5 AUBREY 6 BALTIMORE 7 BANNATYNE 8 BOYLE 9 CLIFTON 10 COCKBURN/CALROSSIE 11 COLONY 12 CORNISH 13 DESPINS 14 DONCASTER 15 DOUGLAS PARK 16 DUMOULIN 17 FERRY ROAD 18 HART 19 HAWTHORNE 20a JEFFERSON EAST 20b JEFFERSON WEST 21 JESSIE 22 LAVERENDRYE 23 LINDEN 24 MAGER 25 MARION 26 METCALFE 27 MISSION 28 MOORGATE 29 MUNROE 30 NEWTON 31 PARKSIDE 32 POLSON 33 RIVER 34 RIVERBEND 35 ROLAND 36 SELKIRK 37 STRATHMILLAN 38 ST. JOHN'S 39 SYNDICATE 40 TUXEDO 41 TYLEHURST 42 WOODHAVEN 72 Windsor Park CSO_dists; ms\01\ Average Annual Overflows = 7 Range: 2 to Figure 4.22 Location and Size of Combined Sewer Districts To put in perspective the size of these areas, Windsor Park is 404 ha and has a population of roughly 12,300 people. Analysis of 1996 and 2001 census data indicates this population is relatively stable. Water consumption in this district was also analyzed and scaled up 18.5% to account for base infiltration (48 lcd) in the winter. Based on this analysis, the estimated DWF from Windsor Park is about 3.1 ML/d. It is assumed that this will remain constant into the future to the year A similar analysis was done on the four combined sewer districts, which together have a population of 38,430 and an area of 1,475 ha. Water consumption records in these areas were analyzed and scaled up to reflect the 18.5% average infiltration rate across the SEWPCC service area in winter. The analysis produced an estimated DWF of 10.8 ML/d from these four 4.26

28 districts. The estimated DWF from each Combined Sewer District is: Mager Cockburn 6.2 ML/d 2.3 ML/d Baltimore 2.0 ML/d Metcalf 0.3 ML/d The effects of some potential DWF diversions on the projection to the year 2050 are shown in Figure Different combinations of diversions from the combined sewer districts and Windsor Park could provide different projections. Pumping (MLD) MLD 68.4 MLD 57.6 MLD Historic DWF Projection With Out CS Districts 2031 Without Windsor Park District Year Figure Effects of DWF Diversions on Projections to

29 Table 4.10 Effect of Diversions on SEWPCC DWF Projection to 2031 and 2050 Option Base Case (No Diversions) Without Windsor Park District Without Combined Sewer Districts Without Windsor Park & Combined Sewer Districts Estimated SEWPCC Projection ML/d in 2031 Estimated SEWPCC Projection ML/d in Table 4.10 shows the effect of diverting of Windsor Park and the combined sewer districts on SEWPCC DWF for the years 2031 and The range of options considered for the 2031 design year are: The base case year round flow to SEWPCC from Windsor Park and the combined sewer districts giving a design DWF of 68.4 ML/d. Without Windsor Park the DWF would be 65.3 ML/d. Without the combined sewer districts the DWF would be 57.6 ML/d. Without Windsor Park and the combined sewer districts the DWF would be 54.5 ML/d. These options give considerable flexibility to the City when considering how to divert wastewater. The merits of diverting wastewater depend upon other factors such as treatment processes at the SEWPCC and the NEWPCC, as well as sewer system capacity throughout both districts and the ability to convey to each of the plants without causing hydraulic problems in the system or unnecessary overflows Hourly DWF Peaking Using the six-minute pumping records ( ) from SEWPCC an analysis was done on the diurnal variation of dry weather flow during a mid-winter period (February 2005). Figure 4.24 illustrates the SEWPCC flow pattern in the chosen period. This figure shows diurnal flow with two peaks during week days and one peak during weekends. An analysis of this pattern indicates that the hourly peaking factor is in the range of 1.5 to 1.6 for the SEWPCC service area. The lowest diurnal flow is about 40% of the DWF. 4.28

30 120 Flow at SEWPCC (ML/d) Sunday Monday Tuesday Wednesday Thursda y Friday Saturda y Figure Weekly Flow Pattern (February 2005) Wet-Weather Flow (WWF) Projections Introduction WWF projections are required to determine WWF peaks at the SEWPCC during two distinct periods of the year: During the spring melt, flows can stress the system hydraulically and, as well, cold inflows entering the system can drive the temperature down, stressing the biological treatment. Year-round or summer peaks can stress the system hydraulically. In the past, WWF has been described by using a peaking factor. This peaking factor is multiplied by the projected DWF to indicate what the peak flow in the system will be in the future. Since DWF projections in this study are based on a projection that considers water conservation, per capita DWF will be shrinking in the future. The factors that affect WWF are independent of the factors that affect DWF, therefore estimating WWF as a multiple of DWF is inappropriate and could under estimate peak flow design requirements. In this study the WWF and DWF analyses have been separated and each is projected independently. For WWF, the analysis also considered variability of possible future conditions. At any given year in the future, there is a probability that a certain design flow will be exceeded 4.29

31 A simple frequency analysis performed by calculating the estimated return period for each of the maximum annual WWFs. This frequency analysis was done for both spring and year- round periods. Spring was defined as WWFs between March 1 and April 30. due to WWF. The design of the plant can be based on selecting an appropriate design frequency and duration of event Policy Decision Various design flows need to be selected for components at the SEWPCC. The design flows should be based on realistic assumptions of return period and duration of flow to be handled Frequency Analysis The methods used to analyze dry-weather flow to determine the frequency in the future were as follows: WWF at the SEWPCC for each day was estimated by subtracting the DWF estimate for each year (based on winter pumping rates) from the total daily flow. Once the daily WWF for each year was estimated, the per capita WWF was estimated by dividing by the historic population for that year. This analysis was done on pumping records from 1983 to The next step was to calculate the moving average WWF for several averaging periods; the 30-day moving average and a 7-day moving average were considered in addition to the daily (i.e., 1-day average) WWFs. For each year, the maximum WWF was identified for each of the 1-, 7- and 30-day moving averages. To design pumping at the treatment plant, it is expected that the collection system will bring 1:5- year one-day events to the SEWPCC which will need to be handled. A 1:5-year frequency event is realistic since the this is the frequency of the sewer designs to prevent basement flooding. It is expected that when flows are higher than a 1:5-year maximum day, overflows will occur in the system and therefore will not be transported to the SEWPCC. This decision was agreed upon with the City at the July 6, 2006 workshop. The frequency plots for SEWPCC WWF (in lcd) for both spring and year-round periods are shown in Figure 4.25 and Figure

32 1,200 WWF (lcd) 1, Maximum Day Max. 7-Day Moving Avg. Max. 30-Day Moving Avg % 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Probability of Not Being Exceeded Figure Spring WWF Frequency 1,600 WWF (lcd) 1,400 Maximum Day Max. 7-Day Moving Avg. 1,200 Max. 30-Day Moving Avg. 1, % 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Probability of Not Being Exceeded Figure 4.26 Year-Round WWF Frequency 4.31

33 Flow Frequency Distribution in 2031 Based on Historic Data Analysis Based on historic data, WWF probability distributions for the 2031 design year were developed. Figure 4.27 shows the expected distribution for spring peak flows and Figure 4.28 shows the year-round peak flow distribution. SEWPCC Flow (MLD) SEWPCC 2031 Spring Maximum Day data Max. 7-Day data Max. 30-Day data 0 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Frequency Not Exceeded Figure Expected Distribution for Spring Peak Flows 600 SEWPCC Flow (MLD) Maximum Day Max. 7-Day Max. 30-Day data data data 0 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Probability of Not Being Exceeded Figure Expected Distribution for Year-Round Peak Flows 4.32

34 Accounting for Potential Sanitary Sewer Overflows (SSO) Planning-level analysis was performed to understand whether major SSOs may be occurring during high WWFs and whether this would impact the frequency analysis of WWFs developed previously. An analysis of past records and pumping capacities throughout the SEWPCC collection system was performed in order to estimate potential historic SSOs. This information was then used to determine what WWF could be in the future if these SSOs were captured and brought to the SEWPCC. Some key assumptions were made to do this analysis: The first assumption was that I/I occurs uniformly across the South End collection area (Note: An I/I study occurring at this time is monitoring I/I throughout the system and will be able to develop actual numbers on I/I and will allow this assumption to be refined). It is assumed that in the future the rate of inflow from the combined sewer overflows (CSO) districts will be maintained at the current 41.5 ML/d. The assumption is that CSO control will involve a strategy that will store the combined sewage and dewater it at a rate of 41.5 ML/d. If the pumping at the Mager district is increased from 41.5 ML/d, the peaks at the SEWPCC would increase by the same amount. To develop the SSO analysis, the capacity of the pump stations throughout the area that contribute flow to the SEWPCC were obtained and the tributary area for each of these pump stations was estimated. The tributary area was estimated by reviewing air photos to estimate the percent of actual developed area in each of the subcatchment areas. The pumping stations and their associated tributary areas estimated were: The CSO districts (Mager, Baltimore, Cockburn/Calrossie). The maximum pumping limit at Mager is 41.5 ML/d. D Arcy pumping station includes the separated area west of the river and south of the Crane/Willow districts. Pumping capacity for this area is assumed to be 90 ML/d. The Crane and Willow areas are sanitary sewer areas without sump pumps. Crane, which accepts Willow District flows, has a pumping capacity of 20.6 ML/d. A Windsor Park separate sewer also does not have any major sump pump area. The pumping capacity to the interceptor for Windsor Park is assumed to be 10 ML/d. The rest of the area that has been designated as South St. Vital/South St. Boniface includes some sump pump areas such as Pulberry; however, it is assumed that there is no pumping limitations in this area. Figure 4.29 shows the 2005 major pump areas in the SEWPCC catchment area. 4.33

35 Figure Pumped Areas in the SEWPCC Catchment The analysis has determined that the CSO districts will be the first areas to have pumping limitations. As expected, combined sewer overflows will occur first, before any sanitary sewer overflows. Windsor Park becomes limiting at 10 ML/d when the expected pumping rate at the SEWPCC is 160 ML/d. The next major limitation in the area was at the D Arcy pumping station, which, assuming I/I is distributed evenly across the area, would become limiting at 90 ML/d. At this time, the flow to the SEWPCC will be 245 ML/d. Therefore, when flows at the SEWPCC exceed 245 ML/d, we would expect that D Arcy will be overflowing. The Crane/Willow Districts become limiting at 21.6 ML/d when the SEWPCC pumping rate is at 250 ML/d. No other system is expected to become limiting before the SEWPCC pumping rate of 364 ML/d (the capacity of SE WPCC) is met. Figure 4.30 illustrates the flow arriving at the SEWPCC with the expected flow that could be arriving at the SEWPCC without SSOs. The difference between the two lines is the amount of SSOs occurring, either at D Arcy or at Windsor Park. It is likely that the vast majority of the SSO volume occurs at D Arcy (50-80%). Using this relationship, the hourly flow record at the SEWPCC for a July 2005 event (the week of June 26 to July 2, 2005) was adjusted. Figure 4.31 illustrates the adjustment occurring during the major storm in July of This adjustment indicates that during peak flows at SEWPCC when 350 ML/d is occurring, an SSO of as much as 105 ML/d could be occurring. Most of this (80 ML/d) is expecte d to occur at D Arcy. With no limitations in the system the flow at the SEWPCC could be as high as 4.34

36 455 ML/d. This analysis was also done for the spring of 2006 and for events occurring in the spring of 2005, the summer of 2004, the summer of 2002 and the summer of The estimated amount of SSOs occurring during these events for the maximum hour and for the maximum day was calculated. The flows for the largest events occurring in each year were adjusted upward. Table 4.11 shows the adjustments in maximum hourly and maximum daily flows for major events occurring over the past ten years. Table 4.11 Adjustments to Peak Flows to Account for SSOs Hour Peak (ML/d) Day (ML/d) Events Peak SSO Estimate Adjusted SEWPCC¹ Peak SSO Estimate Adjusted SEWPCC¹ Peak Factor Max Hour/ Max Day Comment From 2000 TetrES Analysis 1997 Spring Assume 50% Shed Records Estimate 2004 Spring Records 2004 Summer Records Records Spring Records -Not used 1.69 in Freq Analysis 1.60 Average 1) To consider full capture of SSOs Note: these could change with better I/I information expected from SE I/I study This analysis was used to adjust each of the flows in the frequency analysis done presented in the previous section. Figures 4.32 and 4.33 illustrate the adjusted frequency analysis for both year-round and spring events. Only the maximum daily flows are large enough to be impacted by this analysis. The longer duration (7-day, 30-day) frequency analysis is not expected to be different when accounting for SSOs. 4.35

37 Potential Total Flow (ML/d) Existing System no SSO SEWPCC (ML/d) Figure Flow Arriving at SEWPCC and Expected Flow Without SSOs 2005 Summer Total Flow SEWPCC (ML/d) Flow at SSO Summer WWF DWF Sunday Monday Tuesday Wednesday Thursday Friday Saturday Figure Adjustment During 2005 Summer Storm 4.36

38 700 SEWPCC Flow (MLD) Maximum Day SSO Occurring Maximum Day Max. 7-Day Max. 30-Day SSO adjusted data data data data 0 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Probability of Not Being Exceeded Figure Frequency Analysis Accounting for Potential SSOs Annual in SEWPCC Flow (MLD) Maximum Day SSO Occurring Maximum Day Max. 7-Day Max. 30-Day adjusted data data data data 0 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Frequency Not Exceeded Figure Frequency Analysis Accounting for Potential SSOs Spring in

39 Estimated Hourly Wet-Weather Peak The hourly and daily flow records for the past five years were analyzed to determine a peaking factor to estimate hourly flow based on the daily maximum flow. On average, the wet-weather hourly peaking factor was 1.6 times the maximum flow each year. To estimate the frequency of maximum hourly events for each year, multiply the maximum day event times Sensitivity Analysis of Limiting I/I in New Areas The areas which are being developed after 2006 are expected to have less I/I than the average across the existing SEWPCC service area. Sensitivity analysis was done to determine how less I/I in these areas would reduce the peak flows to the plant during wet-weather conditions. The peak flows for the 1:5 maximum day event in 2031 were modified for various limited I/I scenarios are presented in Table For a 1:5 maximum day event in 2031, assuming the I/I in the new areas is limited to 25% of the I/I currently across the SEWPCC service area, would be 300 ML/d. The first spring under the same conditions, the peak flow would be 237 ML/d. Maximum hour event entering the SEWPCC sewer system would be expected to be 480 ML/d (1.6 x maximum day). Table Effects of Limiting I/I in New Areas for 1:5-Year Maximum Hour and Maximum Day Events in 2031 New Areas Per Max Hour Maximum Day Cent of Current WWF (1.6 X Day) WWF Year WWF Spring 100% % % % % % % % % % % % % % % % % % % % %

40 WWF Diversions If the combined sewer districts and/or Windsor Park are diverted during the summer months then peak flows could be reduced. All of the combined sewer districts in the SEWPCC pass through the Mager District Pumping Station. The City estimated the capacity of this station at 41.5 ML/d. Wet-weather peak events could be reduced by diverting combined sewage to the NEWPCC. For Windsor Park, the total pumping rate to the SEWPCC is assumed to be 10 ML/d. The impact of diverting these districts on peak SEWPCC flows can be determined by subtracting these maximum pumping rates from the estimated design peak flows. The maximum day peak flow is estimated at 309 ML/d for the SEWPCC area. Diverting the combined sewer districts may decrease this to about 270 ML/d. An additional diversion of the Windsor Park district may reduce this to 260 ML/d. The benefit of WWF diversions are complex and must be considered in the context of other studies such as the NEWPCC Master Plan and CSO Control studies Maximum and Minimum Flows A summary of peak summer and spring thaws for maximum hour, maximum day, seven-day, and 30-day averages are shown in Table The historic flow data ( ) was reviewed to develop SEWPCC maximum winter and minimum flow factors. The minimum month, week and day flows for winter, spring and summer were determined from the distribution of annual historic values for these averaging period on a litres/capita/day basis for each season. The seasonal values with a 20% (1 in 5 year) probability of not being exceeded were identified along with the median of annual DWF. The multiplication factors are the ratio of the seasonal flow and the median DWF. The maximum winter and minimum design flows are calculated by multiplying the 2031 DWF by the various factors. The spring and summer flows were determined based on assumption for I/I for the future. Table 4.13 summarizes the maximum and minimum flow factors. 4.39

41 Table Estimated Maximum and Minimum Flows in 2031 Factors Flow (ML/d) Winter Spring Summer Winter Spring Summer Average Day Month¹ Max Week¹ Day¹ Hour¹ Month² Min Week² Day² Hour² Notes 68.4 ML/d is the adjusted DWF for 2031 Max/Min hourly flows are determined relative to the corresponding Max/Min daily flow 1) Maximum flows in Spring and summer are based of assumption for I/I for the future. This is discussed in an earlier sub-section. Peak factors analysis was not used to develop this flows 2) Minimum month, week, day factors based on SEWPCC historic data (on L/c/d basis) and: factors = (minimum flow with a 20% (i.e., 1 in 5 year) probability of not being exceeded) / (median ADWF). 4.40